The invention relates to rotary printing machines in general, to one or more printing plates thereof and more particularly to a method of and apparatus for adjusting the leading, tensioning rail of tensioning devices in the printing plate support cylinder of a rotary printing machine.
In rotary printing machines, thin, flexible printing plates are used. Usually, one or more plates are mounted under tension on a plate support cylinder. The ends of each of the printing plates are bent away in an accurately registering manner and the ends are inserted into tensioning devices formed in the plate cylinder. Tensioning rails are formed as part of the tensioning device. These rails have a generally beak shaped portion, and the printing plate ends are secured over these beak-like portions. There are a leading tensioning device and its tensioning rail at the leading or forward end of the printing plate (as the cylinder rotates) and a trailing tensioning device and trailing tensioning rail at the trailing end of the printing plate. The tensioning of the plate is usually effected by means of the trailing tensioning rail. The leading tensioning rail determines the position of the printing plate on the printing cylinder. The leading rail must be adjusted in a perfectly registering manner, particularly in multiple color printing.
The adjustment in an accurately registering manner of the leading tensioning rail may be disturbed by initial manufacturing tolerances and by division faults that become noticeable in the tensioning device, as well as in the receiving grooves for the tensioning device in the plate cylinders.